The present invention relates generally to non-invasive diagnoses of medical implants, and more particularly to an ultrasound technique for the in-vivo detection of particulate wear debris from medical implants.
Various types of medical implants have been developed over the years. In many instances, such implants enable humans to live longer, more comfortable lives. Implants such as pacemakers, artificial joints, valves, grafts, stents, etc. provide a patient with the opportunity to lead a normal life even in the face of major heart, reconstructive, or other type surgery, for example.
It has been found, however, that the introduction of such medical implants can sometimes lead to complications. For example, the human body may reject the implant which can ultimately lead to osteolysis or other types of complications. Alternatively, the implant may malfunction or become inoperative.
In the case of some implants such as artificial joints, the implant is subjected to everyday motion, stress and strain. This often leads to abrasion between different parts of the implant, between the implant and the skeletal frame, etc. Such abrasion results in the formation of wear debris particles in the area of the implant which can lead to complications. For example, in the case of an artificial hip joint, wear debris particles from the acetabular cup may build up over time. These wear debris particles can trigger a response of the human body immune system. Because the wear debris particles typically consist of artificial materials which are nonbiodegradable, the immune system attacks on the particles fail. This leads to further increases in immune system enzyme concentration and ultimately resorption of bone by the tissue, a process called osteolysis. The patient can experience a loose joint and pain.
It is desirable therefore to be able to monitor the condition of a medical implant, particularly in the case of an implant which is subject to the generation of wear debris particulate. On the other hand, it is highly undesirable to have to perform invasive surgery in order to evaluate the condition of the implant. Such invasive surgery is not only time consuming, but also costly and painful to the patient.
In view of the aforementioned shortcomings, there is a strong need in the art for an apparatus and method for detecting and evaluating wear debris particulate associated with a medical implant, particularly with respect to an artificial joint. Even more particularly, there is a strong need for an apparatus and method which can evaluate wear debris simply, reliably and non-invasively. Having the capability to detect such debris at an early enough stage would allow physicians to intervene with pharmaceuticals or otherwise before significant bone deterioration or other complications occur.
An apparatus and method are provided for the in-vivo detection of particulate wear debris from medical implants such as artificial joints for hips, knees, shoulders, elbows, etc. According to the invention, a focused ultrasound transducer placed in contact with the body insonifies a region of the body suspected of containing wear debris particulate. Such wear debris particulate may have linear dimensions on the order of 0.1 to 10 microns, for example. The particles are detected by the same or different transducer when cavitation events represented by bursts of scattered ultrasound with amplitudes orders of magnitude higher than background noise levels are received from the particles.
Applicants have found both a particle size and a concentration effect on the amplitude and number of the cavitation events. The cavitation events are believed to be linear and to result from small irregularities in the particle/liquid interface which trap microscopic volumes of gas that serve as cavitation nuclei. Computer analysis of the signal strength (i.e., amplitude) and number of cavitation events and the use of a lookup table or neural network, for example, provide a measurement of particulate distribution (size and concentration) in the vicinity of the implant.
According to the present invention, a system is provided for detecting wear debris particulate from a medical implant within a body of a living animal. The system includes an acoustic transmitter for transmitting acoustic energy from outside the body to a soft tissue region proximate the medical implant generating wear debris particles; an acoustic receiver located outside the body to detect resultant acoustic energy scattered by the wear debris particles and produce a received signal indicative thereof; a processor for processing the received signal to evaluate at least one parameter associated with the wear debris particles; and an output for indicating the at least one parameter.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.